Three leg fractional turn transformer with winding leads and insulation between core parts



O. KlLTlE 3,132,318 TURN TRANSFORMER WITH WINDING ,May 5, 1964 E THREE LEG FRACTIONAL LEADS AND INSULATION BETWEEN CORE PARTS Filed Jan.

INVENTOR- ORDEAN KILTIE ATTORNEYS United States Patent 3,132,318 THREE LEG FRACTIONAL TURN TRANSFORMER WITH WINDING LEADS AND INSULATION BETWEEN CORE PARTS Ordean Kiltie, Fort Wayne, Ind., assignor, by mesne assignments, to Ballastran Corporation, Fort Wayne, Ind, a corporation of Indiana Filed Jan. 8, 1962, Ser. No. 164,937 4 Claims. (Cl. 336-172) This invention relates generally to transformers, and

more particularly to a transformer construction wherein precise turns ratios are provided between the primary and secondary windings.

A transformer conventionally comprises a core formed of magnetic material with two or more coils or windings positioned thereon, the windings being interlinked by the magnetic flux passing through the magnetic circuit formed by the core. I With one of the windings, ie, the primary winding, being connected to a source of alternating current, the output voltages developed in the other windings, i.e., the secondary windings, neglecting losses, are in direct proportion respectively to the turns ratios between the secondary windings and the primary winding; with a secondary winding having twice the number of turns as the primary winding, the output voltage developed in the secondary winding will be twice the supply voltage impressed upon the primary winding.

In the design of most transformers, output voltage within suitable tolerances can be provided by merely selecting the turns ratios of the windings. However, in certain applications, particularly in transformers for instrumentation and computers, it is required that very precise output voltages be provided. In the case of transformers having only one secondary winding, the provision of the requisite precise output volt-age is not difiicult since selection of an appropriate number of turns for the primary and secondary windings respectively will provide an infinite number of turns ratios and thus output voltages. However, when more than one output voltage is required and these must be held to very precise tolerances, it frequently has been impossible to provide the requisite precise output voltages with a single transformer having more than one secondary Winding; if the turns ratio of the primary winding and one secondary winding is selected to provide one of the required output voltages, the addition of a full winding turn on the other secondary winding may provide too high an output voltage and the subtraction of one full turn may provide too low an output voltage. For this reason, it has been frequently found necessary to employ a plurality of transformers to provide sufiiciently precise output voltages with resulting increase in the size, weight and cost of the apparatus in which the transformers are incorporated.

In order to provide a transformer having very precise output voltages, particularly where more than one output voltage and thus more than one secondary winding is required, provision of the proper turns ratio may require that one or more of the windings have a fractional turn, i.e., less than a full winding turn surrounding a portion of the core. While trans-former constructions have been proposed in which a fractional turn was provided on a winding, to the best of the present applicants knowledge, such proposals have not been applicable to conventional transformer constructions of the type employed for instrumentation and computers and/or could not readily be employed in quantity production.

It is accordingly an object of my invention to provide an improved transformer construction wherein a fractional turn is provided on at least one of the windings. on at least one of the windings and which is suitable for Another object of my invention is to provide an improved transformer construction having a fractional turn quantity production.

A further object of my invention is the provision of an improved transformer construction of the type employed in instrumentation and computers and having a fractional turn on at least one of the windings.

Further objects and advantages of my invention will become apparent by reference to the following description and the accompanying drawing, and the features of novelty. which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

My invention in its broader aspects provides a transformer having a laminated magnetic core structure formed of at least two transversely spaced sections, the core defining a coil-receiving window. Insulating means is provided transversely spacing the core sections and a first coil is positioned on a portion of the core and extending through the window, the first coil having a predetermined number of full winding turns. A second coil is provided positioned on aportion of the core and extending through the window, the second coil also having a predetermined number of full winding turns. The inand the window. The second coil has a lead or end with one portion thereof extending into the window and another portion extending outwardly from the window through the opening in the insulating means so that the one portion on the second winding end extends across only one section of thecore thereby forming a fractional winding turn on the second coil.

In the drawing, FIG. 1 is a view in perspective of a transformer incorporating my invention;

FIG. 2 is a top view of the transformer of FIG. 1; and

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 2.

Referring now to FIGS. 1, 2 and 3 of the drawing, my invention is shown embodied in a transformer, generally indicated at it having a magnetic core 12 of the shell type, transformer 10 being of the type commonly employed lfor instrumentation and electronic applications. The magnetic core 12 is formed of a plurality of abutting E-shaped laminations '14 and I-shaped laminations 16 of relatively thin magnetic steel, the E-shaped laminations 14 and I-shaped laminations 16 being interleaved in accordance with conventional practice. The E-shaped laminations 14 each have a center winding leg 18 joined to an end leg 26 which in turn has side legs 22 and 24 joined thereto, the I-shaped laminations 16 abutting the 3 ends of the center leg 18 and the side legs 22, 24, as best seen in FIG. 3. When the laminations comprising the core 12 are assembled, it will be seen that winding windows 26 and 28 are defined thereby.

The E-shaped and I-shaped laminations 14, 16 of core 12 in the illustrated embodiment are divided into three transversely spaced-apart groups or sections 30, 32 and 34, these groups or sections being of predetermined relative transverse height as will hereinafter be more fully explained. The core sections 30, 32 and 34 are respectively transversely spaced-apart by side insulators 36 and 38 formed of suitable insulating material which respectively extend between the top and bottom surfaces of the core and are coextensive in width and respectively in alignment with the side legs 22, 24. The core sections 30, 32 and 34 are also spaced-apart by center insulators 40 and 42 which are respectively coextensive in width and in alignment with the center winding legs 18. The center insulators 40, 42 respectively have bottom edges 44 in alignment with the bottom side of the core 12 and top edges 46 having rounded corners 48 and which are recessed from the top side of the core 12 to define slots 51 and 49 with the adjacent laminations.

Positioned on the center winding legs 18 of the core 12 is a coil 50 having sides 52 and 54 respectively extending through the winding windows 26, 28 and having ends 56 and 60 respectively disposed on the outer faces of the center winding leg of the core 12 defined by the center lamination legs 18. Coil 50 has top and bottom sides 62 and 64 respectively closely spaced from the end legs 16, 20.

Coil 56, which in the illustrated embodiment is formed of a primary and two secondary windings wound one over the other, is in accordance with conventional practice pre-wound on a suitable winding form of insulating material with the center legs 18 of the E-shaped laminations. 14 then being alternately inserted in the two open ends of the coil, as is well known to those skilled in the art. Coil 50 is secured on the center leg of the core against vibration by means of center legs 65 of E-shaped keeper or end laminations 66 having end legs 68 and side legs 70; end laminations 66 have the same configuration as the E-shaped laminations 14 of core 12 however with their side legs 70 and center legs 65 extending the full height of the core. End laminations 66 are preferably formed of metal, not necessarily magnetic, and may be thicker than the laminations 14, 16. The laminations 14, 16, the insulators 36, 38, 40 and 42, the coil 50, and the end laminations 66 are held in assembled relation by means of suitable through-bolts 72 extending through suit. able holes in the laminations and the insulators adjacent the corners of the core in accordance with conventional practice.

In the illustrated embodiment, coil 50 is formed of two secondary windings 74, 76, and a primary winding 78 wound one over the other in accordance with conventional practice; the particular arrangement of the windings on the center leg of the core is not important and thus, the primary winding 78 may equally well be the center winding or an intermediate winding rather thanthe outer winding.

Primary winding 78 has a pair of leads or ends 80 and 82 connected respectively to the ends of the turns of wire forming primary winding 78, leads 80 and 82 extending to the source of energizing potential. In the illustrated construction, in order to provide the requisite fractional turn, lead 82 which is attached to the wire forming winding 78 on end 60 of coil 50 at top surface 62, extends into window 26 between top surface 62 and end leg of core 12, upwardly through the space 84 between the adjacent laminations of groups 32 and 34 and between adjacent side insulator 38 and center insulator 42, over the upper end 46 of the center insulator 42 entirely within the slot 49, i.e., below the outer side of core 12, downwardly through the space 86 defined between the adjacent lamina- 4 tions of groups 32 and 34 and between the adjacent side insulator 38 and center insulator 42 into window 28, and outwardly between the upper face 62 of coil 50 and leg 20 of core 12 to end 60 of the coil, as shown.

It will now be seen that lead 82 has a portion 88 which is disposed in the slot 49 and which extends generally parallel to the path of magnetic flux in the end leg 20 of core 12, the portion 88 being respectively joined to two portions and 102, which extend under the end leg laminations 20 of groups 30 and 32 and transversely thereto. Thus, current flowing in portion 88 of lead 82 does not contribute to the magnetic field established in core 12 by the full turns of primary winding 78 to any material degree, however, it will be observed that the two portions 100 and 1102 of lead 82 which extend through windows 26 and 28 transversely with respect to the laminations of groups 30 and 32 form a winding turn which however embraces only a fractional part of the overall height of core 12. Thus, the ampere-turns contributed by the winding turn defined by lead 82 will be a fractional part of the ampere-turns contributed by one full turn of primary winding 78 in the same proportion as the height of the laminations of groups 30 and 32 to the total height of all the laminations of the core. Thus, the winding turn defined by the lead 82 is a fractional turn with respect to the full turns of primary winding 78.

In the illustrated embodiment, secondary winding 76 has a pair of leads or ends 90 and 92 adapted to be connected to a load. -End 92 likewise is connected to the wire forming the full turns of secondary winding 76 on end 60 and upper face 62 of core 50. Lead 92 extends into window 26 in the space between upper face 62 of core 50 and end legs 20 of core 12, upwardly through the space 94 defined between the adjacent laminations of groups 30 and 32, over the upper end 46 of the center insulator 40 in the respective slot 51, downwardly in the space 96 between the adjacent laminations of groups 30 and 32 into the window 28, and out of the window 28 in the space defined between the top face 62 of coil 50 and end laminations 20, again to the same side of core 12 as its point of connection to the wire forming the turns of secondary winding 76. Here, top portion 98 of lead 92 is again generally parallel with the path of the magnetic flux in the core and thus no appreciable voltage will be induced therein. Portions of lea-d 92 however extend transversely with respect to the end laminations 20 of group 30 thus forming a winding turn, which, in common with the turn formed by lead 82, of primary winding 78, embraces only a fractional part of the total height of the core 12. Thus, the voltage induced in the winding turn defined by lead 92 will be a fractional part of the voltage induced in one full turn of secondary winding 76 in the same proportion as the height of the laminations of groups 30 to the total height of all the laminations of the core.

In a particular transformer construction incorporating my invention having an overall stack height of core 12 of 1.346 inches including insulators 36, 38 and 40,, the insulators 36, 38 and 40. were respectively one-sixteenth inch in thickness and thus the total height of the laminations forming the core was 1.222 inches. In this transformer intended for operation from a -vo1t source of single-phase, 400-cycle alternating current, it was specified that the low voltage secondary winding have a voltage ratio of .26087 plus or minus .00013 and that the high voltage secondary winding have a voltage ratio of 1 plus or minus .005. At first glance, it would have appeared that the primary and high voltage secondary windings could have been provided with exactly the same number of full turns to provide a one-to-one turns ratio and that the low voltage secondary winding could have had a fractional turn added thereto in the manner described above in order to provide the requisite turns ratio. However, if the primary and high voltage secondary windings had been provided with exactly the same number of full turns, the 1R losses in the primary and the secondary windings would have reduced the output voltage to something the order of 114.3 volts which would be outside of the specified ratio and further, in the particular transformer under consideration, the low voltage secondary winding was center-tapped which would have required bringing out both ends in order to provide a fractional turn. For this reason in the illustrated embodiment, low voltage secondary winding 74 was wound with 30 full turns of wire and center-tapped. Primary winding 78 was wound with M4 full turns of wire with the lead 92 providing an additional .717 turn. T o accomplish this, groups 30 and 32 laminations of core 12 had a total height of .877 inch which is .717 of the total height of the stack of laminations of 1.222 inches. High voltage secondary winding 76 was provided with 115 full turns with lead 82 adding .076 turn. .To accomplish this, group 30 of the laminations had a height of .093 inch which was .076 of the total height of the stack of laminations of core 12. From this it can be readily seen that group 32 of the laminations had a height of .784 inch and group 34 had a height of .345 inch.

Leads 104 for the low voltage secondary winding 74 are shown extending from the end 56 of coil 50, but may, however, be brought out at any convenient location.

While in the specific example of my invention described above, the low voltage secondary winding 74 was chosen as the point of reference, i.e., the winding having a predetermined number of full turns, and the primary winding 78 and high voltage secondary winding 76 were adjusted to provide the proper turns ratio, it will be readily apparent that in any given transformer, any winding may be chosen as the point of reference and the other windings adjusted depending upon such matters as relative wire size, center taps, etc. It will be seen that the insulating spacers 36, 38, 40 and 42 may be positioned in any desired location in the stack of laminations to provide the requisite fractional turn, the accuracy of the arrangement being the relationship which the thickness of one lamination bears to the overall height of the stack of laminations. This accuracy may be further increased if need be to half the thickness of one lamination by extending the lead from the full turns of the particular winding through only one of the windows 26, 28 and outwardly through one of the spaces defined between adjacent laminations and without carrying it over the center insulator and returning it through the other window. Center insulators 40 and 42 may be coextensive in length with the height of core 12 thus eliminating slots 49 and 51, with top portions 88 and 98 of leads 82 and 92 thus extending over the top of the core, at the expense however of additional D.C. resistance of the exposed portions of the leads which must be compensated for by the voltage correction method of this invention.

It will be seen that the improved transformer construction of my invention lends itself to quantity production and that the adjustment of the fractional turns of the windings to provide the requisite turns ratio can be conveniently accomplished during final testing and assembly of the transformer; it is not difficult during the final testing to move a set of insulators 36, 40 over by one or more laminations and to rethread the lead through the resulting spaces and slot in order to secure the desired transformation ratio.

While I have illustrated and described a specific embodiment of my invention, further modifications and improvements will occur to those skilled in the art and I desire therefore in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What is claimed is:

1. A transformer comprising: a rectangular magnetic core structure having a central winding leg, end legs joined to said center leg, and side legs respectively joined to said end legs and spaced from said center leg to define coil-receiving windows therewith; said core being formed of a transversely stacked plurality of relatively thinlaminations of magnetic material in at least two transversely spaced groups of predetermined relative transverse height; insulating means respectively spacing said groups and each comprising first insulators respectively in alignment with the laminations forming said side legs and a second insulator in alignment with the laminations forming said center leg, said second insulator having one end thereof spaced from the outer side of the laminations forming one of said end legs and defining a slot therewith parallel with said laminations; a first coil on said center leg having sides extending through said windows and ends disposed on opposite faces of said center leg, said first coil having a predetermined number'of full turns surrounding said center leg; and a second coil on said center leg having sides extending through said windows and ends disposed on opposite faces of said center leg, said second coil having a predetermined number of full turns surrounding said center leg; said coils substantially filling said windows; said second coil having a lead which starts on the end thereof disposed on one face of said center leg and which extends into one of said windows, upwardly from said one window through the space between the laminations of said one end leg defined by said insulating means, through said slot over said one end of said second insulator, downwardly through the space between the laminations of said one end leg defined by said insulating means and into the other of said windows, and out of said other window on the side thereof on said one face of said center leg whereby said lead of said second winding extends transversely across the laminations of said one end leg of only one of said groups of laminations thereby forming a turn on said second coil which is a fraction of a full turn thereof in the same proportion as the transverse height of said one group of laminations to the total transverse height of all of said groups.

2. The combination of claim 1 wherein said first insulators extend between the outer sides of said end legs respectively and are coextensive in width with said side legs respectively, wherein the other end of said second insulator extends to the outer side of the other of said end legs, wherein said second insulator is coextensive in width with said center leg and has said one end thereof curved, wherein said lead of said second coil is entirely within said slot and below said outer side of said one end leg, and wherein said laminations and said first insulators have openings t-herethrough adjacent the corners of said core; and further comprising fastener means respectively, extending through said openings for holding said laminations and insulators in assembled relation.

3. The combination of claim 1 wherein said laminations are in at least three spaced groups of predetermined relative transverse height respectively spaced by said insulating means; wherein a third coil is positioned on said center leg having sides extending through said windows and ends disposed on opposite faces of said center leg, wherein said lead of said second coil extends through the spaces and slot between the laminations of said top leg defined by one of said insulating means, and wherein said third coil has a predetermined number of full turns and a lead which starts on the side thereof on said one face of said center leg and extends into said one NVlDdOW, upwardly from said one window through the space between the laminations of said one end leg defined by another of said insulating means, through the slot defined by the second insulator of said other insulating means, downwardly through the space between the laminations of said one end leg defined by said other insulating means and into the other of said windows, and out of said other window on the side thereof on said one face of said center leg whereby said lead of said third coil extends across the laminations of said one end leg of said one group of laminations and the adjacent group thereby forming a turn on said third coil which is a fraction of a full turn thereof in the same proportion as the transverse height of said one and adjacent groups of larninations to the total transverse height of all of said groups.

4. The combination of claim 3 wherein said coils are wound one over the other, wherein said first coil is a low voltage secondary winding, and wherein one of said second and third coils is the primary winding and the other is another secondary Winding.

References Cited in the file of this patent UNITED STATES PATENTS Burket Oct. 19, 1926 Casper et al May 10, 1927 Kouyoumjian May 23, 1932 Welch May 19, 1942 Chiles et a1. Nov. 29, 1955 FOREIGN PATENTS Germany Sept. 26, 1936 Great Britain Nov. 11, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CQRRECTION Patent N0 3, 132,318 May 5 1964 Ordean Kiltie Itis hereby certified that error appears in'the above numbered patent requiring correction and that the said Letters Patent shouldread as corrected below Column 2, line 9, strike out "on at least one of the windings and which is suitable for" and insert the same after turn" in line 11 same column 2.

Signed and sealed this 22nd day of December 1964.

(SEAL) Aftest:

ERNEST w. SWIDER' EDWARD J. BRENNER Attes'ting Officer Commissioner of Patents UNITED STA'TES'PATENT OFFICE CERTIFICATE OF' CORRECTION Patent N00 3, 132,318 May 5, 1964 Ordean Kiltie It is hereby certified] that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as correc'tedbelow.

Column 2, line 9, strike out "on at least one of the windings and which is suitable for" and insert the same after "turn" in line 11, same column 2.

Signed and sealed this 22nd day of December 1964.

( SEAL) Attest:

ERNEST w. SWIDER' EDWARD J. BRENNER Attes'ting Officer Commissioner of Patents 

1. A TRANSFORMER COMPRISING: A RECTANGULAR MAGNETIC CORE STRUCTURE HAVING A CENTRAL WINDING LEG, END LEGS JOINED TO SAID CENTER LEG, AND SIDE LEGS RESPECTIVELY JOINED TO SAID END LEGS AND SPACED FROM SAID CENTER LEG TO DEFINE COIL-RECEIVING WINDOWS THEREWITH; SAID CORE BEING FORMED OF A TRANSVERSELY STACKED PLURALITY OF RELATIVELY THIN LAMINATIONS OF MAGNETIC MATERIAL IN AT LEAST TWO TRANSVERSELY SPACED GROUPS OF PREDETERMINED RELATIVE TRANSVERSE HEIGHT; INSULATING MEANS RESPECTIVELY SPACING SAID GROUPS AND EACH COMPRISING FIRST INSULATORS RESPECTIVELY IN ALIGNMENT WITH THE LAMINATIONS FORMING SAID SIDE LEGS AND A SECOND INSULATOR IN ALIGNMENT WITH THE LAMINATIONS FORMING SAID CENTER LEG, SAID SECOND INSULATOR HAVING ONE END THEREOF SPACED FROM THE OUTER SIDE OF THE LAMINATIONS FORMING ONE OF SAID END LEGS AND DEFINING A SLOT THEREWITH PARALLEL WITH SAID LAMINATIONS; A FIRST COIL ON SAID CENTER LEG HAVING SIDES EXTENDING THROUGH SAID WINDOWS AND ENDS DISPOSED ON OPPOSITE FACES OF SAID CENTER LEG, SAID FIRST COIL HAVING A PREDETERMINED NUMBER OF FULL TURNS SURROUNDING SAID CENTER LEG; AND A SECOND COIL ON SAID CENTER LEG HAVING SIDES EXTENDING THROUGH SAID WINDOWS AND ENDS DISPOSED ON OPPOSITE FACES OF SAID CENTER LEG, SAI SECOND COIL HAVING A PREDETERMINED NUMBER OF FULL TURNS SURROUNDING SAID CENTER LEG; SAID COILS SUBSTANTIALLY FILLING SAID WINDOWS; SAID SECOND COIL HAVING A LEAD WHICH STARTS ON THE END THEREOF DISPOSED ON ONE FACE OF SAID CENTER LEG AND WHICH EXTENDS INTO ONE OF SAID WINDOWS, UPWARDLY FROM SAID ONE WINDOW THROUGH THE SPACE BETWEEN THE LAMINATIONS OF SAID ONE END LEG DEFINED BY SAID INSULATING MEANS, THROUGH SAID SLOT OVER SAID ONE END OF SAID SECOND INSULATOR, DOWNWARDLY THROUGH THE SPACE BETWEEN THE LAMINATIONS OF SAID ONE END LEG DEFINED BY SAID INSULATING MEANS AND INTO THE OTHER OF SAID WINDOWS, AND OUT OF SAID OTHER WINDOW ON THE SIDE THEREOF ON SAID ONE FACE OF SAID CENTER LEG WHEREBY SAID LEAD OF SAID SECOND WINDING EXTENDS TRANSVERSELY ACROSS THE LAMINATIONS OF SAID ONE END LEG OF ONLY ONE OF SAID GROUPS OF LAMINATIONS THEREBY FORMING A TURN ON SAID SECOND COIL WHICH IS A FRACTION OF A FULL TURN THEREOF IN THE SAME PROPORTION AS THE TRANSVERSE HEIGHT OF SAID ONE GROUP OF LAMINATIONS TO THE TOTAL TRANSVERSE HEIGHT OF ALL OF SAID GROUPS. 